A tool for setting self-cutting undercut anchors where the anchors are formed of an anchor rod with a conically shaped surface at the leading end of the rod widening in the setting direction and a rotatable sleeve placed around the anchor rod and having cutting tabs at the leading end of the sleeve which can be spread radially outwardly as the sleeve is driven against the conically shaped surface so that the cutting tabs form an undercut in the wall surface of a cylindrical borehole in a receiving material as the sleeve is rotated. The tool includes a rotatable propelling part for the sleeve and the propelling part has an insertion end to be placed in a chuck of a rotary hammer drill.
Positively locked anchorages are frequently used for attachment devices exposed to high tensile stresses and, in particular, for attachments for safety applications. As a result of the positive engagement, expansion forces are substantially prevented under load. Accordingly, it is possible to maintain small axial spacing and edge spacing as compared with conventional expansion anchors. For positively locked anchorages, undercut anchors are used including an anchor rod with a conical surface widening in the setting direction and an axially displaceable sleeve which slides over the anchor rod. The end of the sleeve facing the conically shaped surface has a number of segments which can be spread radially outwardly into an undercut in a receiving borehole when the sleeve is pushed against the conically shaped surface, thus establishing the positively locked engagement.
In the majority of known undercut anchors, the undercut must be produced before setting the anchor. Formation of the undercut may be carried out with a complicated drilling tool with which the cylindrical receiving borehole and the undercut are produced in one drilling operation. Such drilling tools, however, are less suited for hard receiving materials in which the borehole is formed. Therefore, a cylindrical receiving borehole is usually produced first and then the undercut is made at the desired depth in a separate operation using a special undercutting tool. Only after the undercut is formed can the undercut anchor be inserted into the receiving borehole. Such a process for forming positively locked anchorages is relatively time consuming and requires special tools, such as collar drills for producing a receiving borehole with a defined depth, a special undercutting device and, often, another device for securing the undercut anchor.
To facilitate the production of positively locked anchorages, undercut anchors have been proposed in which the undercut is not formed until the setting operation is carried out. A self-cutting undercut anchor of this type is disclosed in U.S. Pat. No. 4,702,754. In this known undercut anchor, the segments which spread radially outwardly are constructed as cutting tabs with cutting edges at their free leading ends. To form the positively locked anchorage, the undercut anchor is inserted into a cylindrical receiving borehole. The sleeve is displaced axially against the conically shaped surface while it is rotated during the setting operation, with the conically shaped surface being supported at the base of the receiving borehole. As the sleeve is rotated, an undercut is formed in the surface of the borehole by the cutting edges on the cutting tabs which are spread radially outwardly by the displacement of the sleeve in the axial direction. The depth of the undercut increases to the extent that the cutting tabs are spread outwardly. At the end of the setting operation, the undercut anchor is secured in a positively locked engagement.
To set the undercut anchor, a setting tool is used having a sleeve-shaped propelling part inserted into the receiving borehole against the trailing end of the anchor rod and is provided with rotating drivers which engage in correspondingly shaped slots or grooves in the trailing end of the sleeve. At its leading end, a cylindrical shaft is formed integrally with the propelling part, with the shaft formed as an insertion end for the chuck of a rotary hammer drill. The sleeve-shaped propelling part is axially rotated by the drill and transmits the rotating movement to the sleeve. The axial displacement of the sleeve is effected by axial blows directed against the propelling part by the hammer drill. When this known setting device is used, the conically-shaped surface of the anchor rod must be supported at the base of the receiving borehole. Accordingly, the depth of the receiving borehole must be exactly monitored as it is being formed. Special drilling tools having a depth stop, for example, collar drills, are required for such an operation. Another disadvantage is that the conically shaped surface of the anchor rod can dig into the base of the receiving borehole during the setting operation. As a result, the undercut is formed too deeply in the receiving borehole and, in turn, the undercut anchor is set too deeply in the base or receiving material.